linux-kernel - Re: Help needed to fix section mismatch warnings

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Date:	Sat, 19 Jan 2008 11:52:55 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	akpm <akpm@...ux-foundation.org>
Subject: Re: Help needed to fix section mismatch warnings

On Sun, 6 Jan 2008 15:07:28 +0100 Sam Ravnborg wrote:

> kbuild emit section mismatch warnings when it detects that someone does a
> call from a non-init section to a init section.
> The rationale here is that the init section are discarded at runtime and
> if this call happens after the init section has gone we have an oops.
> 
> This check is planned to be turned into an error soon but we still
> see a bit too many warnings.
> 
> To see the list below build a kernel like this:
> 
> make allyesconfig
> Set CONFIG_HOTPLUG to n
> (In General Setup | Configure standard kernel features | Support for hot-plugable devices)
> 
> Then build the kernel like this:
> make KCFLAGS=-fno-unit-at-a-time
> 
> The flag "-fno-unit-at-a-time" tell gcc to avoid additional inlining which
> otherwise would hide several section mismatch warnings.
> 
> With latest kernel I got 113 warnings and most should fixable.
> Try to look at how other section mismatch warnings has been fixed for inspiration.
> 
> Patches can be cc:ed to me but always send it to the maintainer and lkml.
> 
> 	Sam
> 
> This is the current list of warnings
> 
> WARNING: vmlinux.o(.text+0x1ffd0): Section mismatch: reference to .init.text:register_cpu (between 'arch_register_cpu' and 'arch_unregister_cpu')

> WARNING: vmlinux.o(.text+0x21a39): Section mismatch: reference to .init.text:absent_pages_in_range (between 'reserve_hotadd' and 'unparse_node')
> WARNING: vmlinux.o(.text+0x21ae9): Section mismatch: reference to .init.data: (between 'unparse_node' and 'null_slit_node_compare')

> WARNING: vmlinux.o(.text+0x38b43): Section mismatch: reference to .init.text:idle_regs (between 'fork_idle' and 'fork_traceflag')

Above 4 seem to be mostly fixed in -mm.  I made patches for them
and then checked -mm, so I won't post the patches...


> WARNING: vmlinux.o(.text+0x43524): Section mismatch: reference to .init.text: (between 'timer_cpu_notify' and 'msleep')
> WARNING: vmlinux.o(.text+0x4c6f6): Section mismatch: reference to .init.text: (between 'rcu_cpu_notify' and 'wakeme_after_rcu')
> WARNING: vmlinux.o(.text+0x51cbe): Section mismatch: reference to .init.text: (between 'hrtimer_cpu_notify' and 'down_read_trylock')

I'll post patches for the 3 above.  However, the rcu code in -mm
is quite different, so the rcu patch may have a short life.

---
~Randy
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